Commutator



ZQov. 6, 1951 TROTT 2,574,360

COMMUTATOR Filed July 12, 1950 INVENTOR. Timalfiy Emil,

Patented Nov. 6, 1951 UNl'i'iZD STATES PATENT OFFICE COMMUTATOR Application July 12, 1950, Serial No. 173,347

3 Claims. 1

This invention relates to a switching mechanism and more particularly to a commutator for use in sequentially and repetitively closing and opening a plurality of electrical circuits.

A switch or commutator of this type ordinarily employs a segmented circular conductor to which the various circuits are connected, whi h seg ments are sequentially sensed by a brush, and further employs means for driving either the brush or the segmented conductor relative to the other. However, brushes have a definite contact resistance and are known to wear unequally and can only contact adjacent segments in sequence, and the segmented conductor upon which the brush must slide will not necessarily have the best electrical characteristics if it is to wear Well.

An object of this invention is, therefore, to construct an improved commutator which will avoid the use of segmented conductors and brushes.

A further object is to provide a commutator which, when introduced into a circuit, will not interpose therein the usual resistance and noise characteristic of a sliding brush type of contact.

A further object is to provide a commutator Whose sequence of operation is not restricted to the sequential contact of adjacent segments.

These and other objects of the invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawing; but it is to be expressly understood that said drawin is employed merely to facilitate the description of the invention as a whole and not to define the limits thereof, reference being had to the appended claims for this purpose.

In the drawing:

Fig. l is a front elevation of a commutator constructed in accordance with the invention; and

Fig, 2 is a section on the line 2-2 of Fig. 1.

Referring to the drawing, the commutator is shown to consist of a stationary sun gear 3 about which the planetary gear 4 is driven by the arm 5. The planetary gear 4 is provided with a hub 6 carrying projecting radial switch-actuating arms I which, during their motion, engage the spaced contacts 8 and 9 of the switches 13 and cause them to make contact to thus cauie circuits which may be connected thereto to be made and broken.

As shown in Fig. 2, the sun gear is a casting provided with bosses iii-so that it may be made fast to a structural support, and is provided with a toothed flange H with which the planet gear 4 meshes as it is driven. To facilitate the alignment of the planet gear 4 and sun gear 3, the latter is provided with an opening for receiving an extension of the driving shaft l2 to which the arm 5 carrying the planet gear 4 is pinned.

The switches !3 are mounted on angle brackets H and, by means of the cap screws I5 and nuts IE, are fastened to the pair of rings H and IS, the heads of said screws 15 being recessed in an annular groove Ilia in the face of the gear 3 and the nuts It engaging said brackets Hi to secure them in angularly adjusted positions about said gear. Said rings I! and I8 are arranged to extend about said groove l5a in opposed and spaced relation for the passage of the shanks of the screws l5 therethrough and are secured to the gear 3 by set screws 19. any of the variety of switches such as are provided in relays and the like, or any other type which is actuated by pressure, and may be nor-. mally opened or closed as necessity requires.

In order to function, it is necessary that the pitch circle diameter of the planet gear and sun gear be commensurable; that is to say, that their ratio in some arbitrary unit of measure be a ratio of Whole numbers. This being the case, if the number of teeth on the planet gear 4 are an integral of the sub-multiple of the teeth of sun gear 3 then the planet gear will roll about the sun gear that number of times and always come back to its initial position. An arbitrary index on the planet gear will, once every revolution, coincide with an arbitrary index on the sun gear. As shown in Fig. 1, the sun gear has teeth and the planet gear 30, so that the planet gear will make four revolutions during one excursion about the sun gear. 111 so doing, the free ends of the actuator arms 1 will describe cycloidal paths of a finite nrmber of cusps which will have a locus on a circle determined by the length of these arms. If that circle passes through or beneath the circle upon which lie the contacts 8 and 9 and the switches are positioned to coincide with the cusps of the generated cycloidal path, all of the switches will be cosed once in each revolution of the planet gear about the sun gear by the actuator arms 7 striking and depressing the contacts 8 to engage the contacts 9. No sliding Wear takes place and no brushes are required. The contacts may be designed for the required current carrying capacity and low resistance, and no resistance or noise is introduced into that circuit into which the commutator is interposed.

If, however, the number of teeth on the planet gear is a fractional sub-multiple or the number of The switches It may be,

teeth on the sun gear then the planet gear 4 will roll about sun gear 3 a number of times before returning to its initial position depending on the gear ratio. A pair of indices on these gears may be made again to coincide only after that number of revolutions. Thus, if the planet gear were to have, for example, 96 rather than 30 teeth, the planet gear would make 1% revolutions during each excursion about the sun gear. If the hub 6 were then to carry but two contacting arms 1, 180 apart, only four of the switches on the sun gear would be contacted, at the positions 90, 180 and 270, and the arms would close these switches in the sequence G", 270, 180,90" and 0 so that, in effect, though the motion of the arm and planet gear is clockwise, the sequence of switch operation would be counter-clockwise.

By proper proportioning of the sun and planet gears so that in every case their pitch diameters are commensurable, innumerable sequences may be set up so that the switches i3 may be actuated in any arbitrarily designated sequence. If the pitch diameters of the sun and planet gears are incommensurable, then no two cusps of the generated cycloid would .coincide until the planetary gear had rotated about the sun gear an infinite number of times, and no sequence could be established. 7

By controlling the rate at which the shaft 52 is turned, the repetition frequently with which the desired sequence of the commutator is activated may be completely determined.

To facilitate interchangeability, the planet gear 4 is mounted so that it is held on the spindle 23 by a screw 20 which engages in a slot 2| in said spindle without binding therein, and spindle 28 extends through a longitudinal slot 29 in the arm so as to be adjustable lengthwise of said arm and radially with respect to the gear 3 by means of the adjusting screw 22 in threaded engagement with said spindle.

The dwell of the contacts 8 and 9 may be controlled by adjusting the length of the arms 1. If the arm is such that it is equal to the radius of the planet gear then the cusps will be sharp and the contact made by the switches only momentary. Lengthening the arm would result in generating an epitrochoid form of cycloid whose cusps are looped'and, therefore, the duration of the contact made at the switches will be increased.

What is claimed is:

l. A device of the character described comprising a stationary gear, a planetary gear meshing therewith and rotatable thereabout, an arm supporting said planetary gear for rotation and having a longitudinal slot therein, a spindle extending through said slot and on which said planetary gear is rotatably mounted, means to removably secure said planetary gear on said spindle, means carried by said arm and engagin said spindle to adjust the same and said planetary gear longitudinally of said slot and radially with respect to said stationary gear, contact actuating elements rotatable with said planetary gear, and contacts supported by said stationary gear for engagement by said actuating elements as said planetary gear is rotated.

2. A device of the character described comprising a stationary gear having an annular groove in a face thereof, a planetary gear meshing with said stationary gear and rotatable thereabout, means for supporting said planetary gear for rotation, contact actuating elements rotatable with said planetary gear, spaced ring members secured to said stationary gear face and extending about said annular groove, fastening elements having portions recessed in said groove for adjustment therein in a circumferential direction relative to said stationary gear, brackets secured against said ring members by said fastening elements and adjustable with the latter and relative to said stationary gear, and contacts carried by said brackets for actuation by said actuating elements as said planetary gear is rotated. I

3. A device of the character described comprising a stationary gear having an annular groove in a face thereof, a planetary gear meshing with said stationary gear and rotatable thereabout, an arm supporting said planetary gear for rotation and having a longitudinal slot therein, a spindle extending through said slot and on which said planetary gear is rotatably mounted, means to removably secure said planetary gear on said spindle, means carried by said arm and engaging said spindle to adjust the same and said planetary gear longitudinally of said slot and radially with respect to said stationary gear, contact actuating elements rotatable with said planetary gear, spaced ring members secured to said stationary gear face and extending about said annular groove, fastening elements having portions recessed in said groove for adjustment therein in a circumferential direction relative to said stationary gear, brackets secured against said ring members by said fastening elements and adjustable REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,364,519 Cofiman Dec. 5, 1944 2, ,583 Von. Martens p 1947 

